Systems for detecting cracks in windows

ABSTRACT

A system such as a vehicle may have windows with one or more conductive layers. The conductive layers may form part of an infrared-light-blocking layer or other layer. The infrared-light-blocking layer or other layer may be formed as a coating on a transparent structural window layer such as an outer or inner glass layer in a laminated window or may be embedded in a polymer layer between the outer and inner layers. Segmented terminals and elongated terminals that may extend past two or more segmented terminals may be coupled to the edges of the conductive layers. Using these terminals, control circuitry can apply localized ohmic heating currents and can make resistance measurements on the conductive layers to detect cracks.

This application is a continuation of U.S. patent application Ser. No.15/650,709, filed on Jul. 14, 2017, which claims priority to U.S.provisional patent application No. 62/378,818, filed on Aug. 24, 2016,both of which are hereby referenced herein in their entireties.

FIELD

This relates generally to systems with windows, and, more particularly,to systems such as vehicles having windows.

BACKGROUND

Vehicle windows sometimes include thin films through which ohmic heatingcurrent may be applied to defrost the windows. Impact from road debrisand other objects can damage windows. For example, a thin film layer ina window that is used for heating the window may become damaged. Whenthis damage is left undetected, there is a risk that the thin film willcorrode due to exposure to moisture or that the thin film may notperform properly. Windows that develop small cracks may also be prone tomore extensive cracking.

SUMMARY

A system such as a vehicle may have windows. Control circuitry in thevehicle may make resistance measurements on the windows to detectcracks. The control circuitry may also apply ohmic heating currents tothe windows to heat the windows. The windows may include conductivelayers that are used in making resistance measurements and that are usedin ohmic heating. These conductive layers may form part of aninfrared-light blocking layer or other window layer.

An infrared-light-blocking layer or other layer in a window may beformed as a coating on a transparent structural window layer such as anouter or inner window layer in a laminated window or may be embedded ina polymer layer between the outer and inner layers.

Terminals formed from elongated strips of metal may be coupled to theedges of one or more of the conductive layers in the window. Theterminals may include segmented terminals and terminals that extendacross the entire width or height of the window. Elongated terminals mayextend past multiple segmented terminals. Using these terminals, thecontrol circuitry can apply localized ohmic heating currents and canmake resistance measurements on the conductive layers to detect cracks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illustrative system in accordancewith an embodiment.

FIG. 2 is a cross-sectional side view of a portion of a window inaccordance with an embodiment.

FIG. 3 is a cross-sectional side view of an illustrative layer such asan infrared-light-blocking layer or other layer with one or moreconductive layers that may be incorporated into a window in accordancewith an embodiment.

FIG. 4 is a diagram showing how a window may be provided with elongatedstrips of metal that form terminals through which current may be appliedto a conductive thin-film layer to heat the window in accordance with anembodiment.

FIG. 5 is a cross-sectional side view of an illustrative windowstructure having a conductive layer and an elongated terminal inaccordance with an embodiment.

FIG. 6 is a cross-sectional side view of an illustrative windowstructure having multiple conductive layers each of which is contactedby a respective elongated terminal in accordance with an embodiment.

FIG. 7 is a cross-sectional side view of an illustrative window showinghow a crack may develop that affects an electrical property of thewindow in accordance with an embodiment.

FIG. 8 is a diagram of an illustrative window showing how elongatedterminals may extend across the upper and lower edges of the window inaccordance with an embodiment.

FIG. 9 is a diagram of an illustrative window showing how elongatedterminals may extend along the left and right edges of the window inaccordance with an embodiment.

FIG. 10 is a diagram showing how horizontally extending and verticallyextending elongated terminals may be segmented in accordance with anembodiment.

FIG. 11 is a flow chart of illustrative operations involved in using awindow with crack detection and heating capabilities in accordance withan embodiment.

DETAILED DESCRIPTION

A system may have windows with one or more structural layers such aslayers of glass or rigid plastic. For example, a window may have anouter structural layer such as an outer glass or plastic layer that islaminated to an inner structural layer such as an inner layer of glassor plastic using a layer of polymer. To provide the windows with desiredoptical properties, additional structures may be incorporated into thewindows. These additional structures may include dielectric thin films,conductive layers such as thin-film metal layers, layers that formfilters for blocking infrared, visible and/or ultraviolet light, inklayers and other layers for adjusting the outward appearance of part orall of a window, and/or other structures.

It may be desirable to ohmically heat a window to deice and/or defrostthe window. To facilitate ohmic heating, at least one of the layers in awindow may be formed from a conductive material. Current may be appliedto a conductive layer to ohmically heat the conductive layer and therebydefrost and/or deice the window.

A window may develop cracks due to impacts from roadway debris or otherobjects. The conductive layer in a window that is used for ohmic heatingor other conductive layer in a window may be monitored by controlcircuitry in a vehicle. Control circuitry may, for example, apply aknown voltage to a conductive layer while measuring a resulting current.Using measurements such as these, information on the resistance of theconductive layer and/or other electrical properties (capacitance,inductance, etc.) can be gathered. Resistance measurements (or othermeasurements) that are abnormal (e.g., excessively high resistancevalues) are indicative of a crack in the window, so suitable correctiveactions may be taken.

An illustrative system with windows is shown in FIG. 1. As shown in FIG.1, system 10 may be a vehicle having portions such as portions 18 and20. Portion 18 may include wheels 14, a body such as body 12 with achassis to which wheels 14 are mounted, propulsion and steering systems,and other vehicle systems. These systems may be controlled manually by adriver (user) in vehicle 10 or may be autonomous. For example, vehicle10 may have control circuitry that gathers driving data dynamicallyusing light-based sensors, ranging systems based on light and/orradio-frequency signals, circuitry for handling wireless data, and/orcircuitry that gathers other sensor data and wireless data. The controlcircuitry may use an electrically controllable steering system invehicle 10 to automatically drive vehicle 10.

Body 12 may include doors, trunk structures, a hood, side body panels, aroof, and/or other body structures. Seats may be formed in the interiorof vehicle 10. Portion 20 may include windows such as window(s) 16mounted to body 12. Window 16 and portions of body 12 may separate theinterior of vehicle 10 from the exterior environment that is surroundingvehicle 10.

Windows 16 may include front windows on the front of vehicle 10, a moonroof (sunroof) window or other window extending over some or all of thetop of vehicle 10, rear windows on the rear of vehicle 10, and sidewindows on the sides of vehicle 10. Windows 16 may be formed from one ormore layers of transparent glass, clear rigid polymer (e.g.,polycarbonate), polymer adhesive layers, and/or other layers. In somearrangements, window(s) 16 may include laminated window structures suchas two or more transparent layers (glass, rigid polymer, etc.) withinterposed polymer layer(s). The polymer in a laminated window may be,for example, a polymer such as polyvinyl butyral (PVB) or ethylene-vinylacetate (EVA).

Vehicle 10 may include control circuitry 24 and input-output devices 22.Control circuitry 24 may include storage and processing circuitry forsupporting the operation of vehicle 10 (e.g., to support manual and/orautomated driving, to take other actions based on user input, to takeother actions autonomously, etc.). The storage and processing circuitrymay include storage such as hard disk drive storage, nonvolatile memory(e.g., electrically-programmable-read-only memory configured to form asolid state drive), volatile memory (e.g., static or dynamicrandom-access-memory), etc. Control circuitry 24 may also includeprocessing circuitry based on one or more microprocessors,microcontrollers, digital signal processors, baseband processors, powermanagement units, audio chips, application specific integrated circuits,etc.

Processing circuitry in control circuitry 24 may be used to control theoperation of vehicle 10 and the components in vehicle 10 (e.g.,components associated with windows 16 and input-output components 22,etc.). For example, control circuitry 24 can apply signals (ohmicheating currents) to conductive films in windows 16 to ohmically heatwindows 16 or portions of windows 16. Control circuitry can also measurethe resistance of a conductive window layer to identify window cracks.

Input-output devices 22 may be used to gather data for vehicle 10, maybe used to gather information from a user (vehicle occupant, etc.) ofvehicle 10, may be used to provide data from vehicle 10 to externalsystems or a user, and/or may be used in handling other input and outputoperations. Input-output devices 22 may include buttons, scrollingwheels, touch pads, key pads, keyboards, and other user input devices.Microphones may be used to gather voice input from a user and may gatherinformation on ambient sounds. Devices 22 may include ambient lightsensors, proximity sensors, magnetic sensors, force sensors,accelerometers, image sensors, and/or other sensors for gathering input.Output may be supplied by devices 22 using audio speakers, tonegenerators, vibrators, haptic devices, displays, light-emitting diodesand other light sources, and other output components. Vehicle 10 (e.g.,devices 22, etc.) may include wired and wireless communicationscircuitry that allows vehicle 10 (e.g., control circuitry 24) tocommunicate with external equipment and that allows signals to beconveyed between components (circuitry) at different locations invehicle 10.

Light filter layers and other layers may be incorporated into window 16.As an example, an infrared-light-blocking layer may extend over some orall of a window. The infrared-light-blocking layer may be formed fromone or more layers of silver or other metal and/or may include thin-filminterference filters formed from multiple dielectric layers and/or otherlayers). These layers may be formed from thin-film coatings depositedusing physical vapor deposition or other thin-film depositiontechniques, may be applied as a polymer coating (e.g., by spraying,printing, etc.), may be formed by laminating a flexible polymer filmthat includes these layers to window 16, or may be formed using othersuitable fabrication techniques.

Inclusion of light filter layers and other layers into window 16 mayalter the visible light and infrared light transmission of window 16. Asone example, an infrared-light-blocking layer may block 50% or more, 70%or more, or 90% or more of near infrared light (e.g., light withwavelengths from 700-2500 nm, light from 700-1000 nm, other light withwavelengths more than 700 nm or less than 2500 nm, etc.) and may allow100%, 70% or more, 90% or more, or less than 99% of visible light topass.

Infrared light blocking may be desirable to prevent excessive heatbuildup in the interiors of vehicles exposed to sunlight. Visible lightblocking may be used to cut down on transmitted light levels (e.g., toreduce excessive bright light to more desirable brightness levels).

To ohmically heat window 16, control circuitry 24 may pass ohmic heatingcurrent through one or more conductive thin-film layers in window 16.The ohmic heating current will cause the conductive thin-film layers toohmically heat window 16. If desired, one or more of the conductivethin-film layers to which ohmic heating current is applied may beconductive thin-film layers associated with a functional layer in window16 (e.g., an infrared-light-blocking layer, etc.). To monitor for cracksin window 16, control circuitry 24 may measure the resistance of athin-film layer in window 16. The thin-film layer that is monitored inthis way may be a conductive thin-film layer associated with aninfrared-light blocking layer, may be an ohmically heated layer, may bea layer that is not ohmically heated, or may be any other suitablelayer.

A cross-sectional side view of an illustrative window is shown in FIG.2. As shown in FIG. 2, window 16 may include one or more transparentstructural layers such as structural window layers 50. Two layers 50 areincluded in window 16 in the example of FIG. 2, but more than two layersor fewer than two layers may be included in window 16, if desired.Layers 50 may be clear layers of rigid polymer, glass, or othertransparent material. Polymer layer 52 (e.g., a PVB layer, an EVA layer,or other polymer layer) may be used to couple layers 50 together and/orlayers such as layers 50 may be separated by an air gap. Illustrativeconfigurations in which layers 50 are coupled by polymer layer 52 maysometimes be described herein as an example.

One or more layers such as layer 54 may be included in window 16. Theselayers may include diffuser layers (e.g., a translucent sheet ofpolymer, a textured polymer layer coated with a thin transparent metallayer, etc.), a light filter (e.g., one or more metal layers such as oneor more silver layers on one or more inorganic or organic dielectriclayers, a filter formed from a multilayer dielectric stack having layerswith different refractive index values or other multilayer filterstructure that is used to block infrared light, ultraviolet light,and/or visible light, etc.), a tint layer (e.g., an optical absorptionlayer that has a gray color or other suitable color), and/or otherlayers (e.g., adjustable layers, etc.). One or more of layers 54 may beincorporated into window 16 (e.g., on the inner and/or outer surface ofan inner structural layer 50 or on the inner and/or outer surface of anouter structural layer 50), and/or embedded within polymer layer 52(e.g., as a thin metal film, as one or more thin-film coating layers ona polymer film carrier or other substrate layer, etc.).

A cross-sectional side view of an illustrative layer 54 that may be usedin some or all areas of window 16 is shown in FIG. 3. As shown in FIG.3, layer 54 may, if desired, include a thin-film stack such as thin-filmstack 56. Stack 56 may include multiple thin-film layers 58. There maybe, for example, 3-10 layers 58 in stack 56, more than 4 layers 58,fewer than 10 layers 58, or other suitable number of layers. Layers 58may include metal layers (e.g., layers of silver, gold, copper,aluminum, titanium, etc.), dielectric layers (e.g., inorganic layerssuch as oxide layers, polymer layers, etc.), semiconductor layers,transparent conductive layers (e.g., a wide bandgap semiconductor suchas indium tin oxide or other transparent conductive oxides), and/orother layers of material. Stack 56 may be formed directly on structurallayers such as layers 50 of FIG. 2 and/or may be supported by a polymercarrier film or other supporting substrate that is separate from layers50 such as optional substrate 60. Substrate 60 may be a polyethyleneterephthalate (PET) layer or other polymer carrier layer, may includetwo or more polymer layers, and/or may be formed from one or more layersof other materials. In configurations in which stack 56 is formed on oneor both sides of an optional substrate such as substrate 60, layer 54may be attached to one of layers 50 (e.g., using adhesive and/or heatand pressure) and/or may be embedded in polymer layer 52 (FIG. 2).

If desired, layers 58 or some of layers 58 may be configured to serve asan infrared-light-blocking layer (filter). For example, layers 58 maycontain one or more layers of silver, two silver layers, more than twosilver layers, three silver layers, or more than three silver layers. Ifdesired, some or all of these silver layers may be replaced by othermetal layers (e.g., gold, copper, aluminum, titanium, etc.). The silverlayer or other metal layers may be separated by other layers such asinorganic dielectric layers, semiconductor layers, polymer layers,and/or other layers. With configurations such as these, layers 58 (e.g.,the silver layers and/or other metal layers) may serve to block infraredlight (e.g., 80% or more of near infrared light from 700-2500 nm, 90% ofnear infrared light from 700-2500 nm, less than 99% of near infraredlight from 700-2500 nm, etc.) and may either be transparent to visiblelight or may reduce visible light transmission (e.g., visible lighttransmission may be 70% to 100%, may be 70% to 90%, may be 50-85%, maybe less than 90%, may be more than 50%, may be more than 70%, etc.).

In some configurations, some or all of layers 58 (e.g., dielectriclayers formed from metal oxides, silicon oxide, silicon nitride, and/orother materials) may form thin-film interference filters. In this typeof arrangement, layers 58 or some of layers 58 may form a thin-filmstack with dielectric layers that alternate between higher and lowerrefractive index values, a thin-film stack with layers of higher andlower refractive index values and interposed layers with intermediaterefractive index values, and/or a thin-film stack with other patterns oflayers that form a thin-film interference filter. The interferencefilter may be configured to adjust the appearance of window 16, to forma stop-band at near infrared wavelengths (e.g., from 700-2500 nm), toproduce a desired amount of visible light attenuation or to betransparent at visible wavelengths, to block ultraviolet lightwavelengths, and/or to produce other desired optical properties(transmission, reflection, and absorption) as a function of wavelength.

One or more conductive layers in layer 54 (e.g., one or more silverlayers or other metal layers) may be used to carry current throughwindow 16. When it is desired to monitor window 16 for cracks, theamount of current that flows for a given applied voltage (or the voltagethat is produced for a given applied current) can be monitored bycontrol circuitry 24 to determine whether the resistance of theconductive layer is abnormally high. When it is desired to heat some orall of window 16, ohmic heating current may be applied to the conductivelayer(s) by control circuitry 24. The ohmic heating current willohmically heat the conductive layer(s) and thereby heat window 16 todefrost and/or deice window 16. The layer or layers to which signals areapplied to measure resistance may be the same as the layer or layers towhich the ohmic heating current is applied or the layer or layers towhich resistance measurement signals are applied may be partly orcompletely different than the layer or layers to which the ohmic heatingsignals are applied. Resistance measurements may be made during heatingor at other times. Resistance measurement operations may be performedindependently of heating operations or resistance measurements may bemade on a conductive layer to which ohmic heating current is beingapplied (e.g., by measuring voltages resulting across the layer inresponse to application of the ohmic heating current).

FIG. 4 is a diagram showing how one or more conductive layers in layer54 of window 16 may be provided with terminals 62 through which signalsmay be applied by control circuitry 24. Terminals 62, which maysometimes be referred to as busbars or contacts, may be shorted to oneor more conductive layers in layer 54 such as one or more silver layersin an infrared-light-blocking filter, one or more other metal layers inan infrared-light-blocking filter, one or more transparent conductivelayers (e.g., one or more layers of indium tin oxide or othertransparent conductive oxide), or other conductive layers (metal,transparent conductive material, etc.).

Terminals 62 may have elongated shapes as shown in the FIG. 4 example(e.g., terminals 62 may be formed from strips of metal that run alongthe edges of window 16, etc.) or may have other suitable shapes. Thesheet resistance of the metal or other conductive material in terminals62 may be less than the sheet resistance of conductive layer to whichterminals 62 connect. The lower sheet resistance of the conductivematerial of terminals 62 helps spread current along the edges of layer54 before the current I is routed through layer 54 between respectiveterminals 62. In the example of FIG. 4, current I is flowinghorizontally (along dimension X, which may be parallel to the ground).If desired, current I may flow vertically or may follow other paths.

FIG. 5 is a cross-sectional side view of layer 54 in an illustrativeconfiguration in which layer 54 includes at least one conductive layer58C and one additional layer 581 (e.g., a dielectric layer). As shown inFIG. 5, terminal 62 (e.g., an elongated terminal that extends into thepage, parallel to the Y axis) may form an ohmic contact with the edge ofconductive layer 58C. Layers 58C and 581 may be two layers amongmultiple layers 58 in stack 56 (FIG. 3).

If desired, terminals may be electrically coupled to multiple conductivelayers in layer 54. As shown in FIG. 6, for example, layer 54 may havemultiple conductive layers such as conductive layers 58C-1 and 58C-2 andmay have multiple additional layers such as layers 581 (e.g., dielectriclayers). Terminals such as terminal 62-1 may be electrically coupled toconductive layer 58C-1 and terminals such as terminal 62-2 may beelectrically coupled to conductive layer 58C-2. Layers 58C-1 and 58C-2may be shorted to each other (e.g., by electrically coupling terminals62-1 and 62-2) or may be electrically isolated from each other.Crack-detection resistance measurements may be made on layer 58C-1and/or layer 58C-2 and, if desired, ohmic heating current may be appliedto layer 58C-1 and/or layer 58C-2. With one illustrative configuration,resistance measurement circuitry in control circuitry 24 may be used tomonitor one of layers 58C-1 and 58C-2 for abnormally high resistancelevels of the type that are indicative of a crack in window 16 anddriver circuitry in control circuitry 24 may be used to apply an ohmicheating current to the other of layers 58C-1 and 58C-2. If desired, theresistance of both of layers 58C-1 and 58C-2 (and, if desired, theresistance of additional conductive layer(s) in layer 54) may bemonitored. Each conductive layer in layer 54 (e.g. one layer, twolayers, three layers, etc.) may be provided with a different respectivepair of terminals 62 and/or two or more conductive layers in layer 54may be shorted together at the edges of layer 54 by shorting theirterminals together. In some arrangements, a conductive layer in layer 54may be formed from multiple conductive sublayers (e.g., metal layers,conductive oxide layers, etc.) that are stacked directly on top of eachother.

A cross-sectional side view of an illustrative edge portion of window 16is shown in FIG. 7. In the example of FIG. 7, window 16 has outer andinner structural window layers 50 and has a polymer layer (e.g., a PVBor EVA layer, etc.) such as layer 52 that is interposed between layers50 to couple layers 50 together. Terminals such as terminal 62 may becoupled to one or more conductive layers in layer 54. Layer 54 may beformed from a single layer (e.g., a single silver thin-film layer or asingle layer of another metal) and/or may be formed from multiple layersof material as described in connection with FIG. 3. Opaque masking layer70 may form an opaque border around some or all of the peripheral edgesof layer 16. Layer 70 may be formed from a ceramic frit containingpigments such as black particles to render layer 70 opaque, a polymerthat contains pigments or dyes (e.g., a polymer that contains blackparticles to render layer 70 opaque), and/or may contain a thin-filminterference filter stack formed from multiple thin-film coatings. Thepresence of masking layer 70 in the border of window 16 may help toenhance the appearance of window 16 in vehicle 10 (e.g., by hidingterminals such as terminal 62 and/or other structures below theoutermost layer of window 16 from view).

During use of vehicle 10, road debris or other external objects maystrike exterior surface 74 of the outer structural window layer 50,thereby creating cracks such as crack 72. Crack 72 may extend into theconductive layer or layers in layer 54. When crack 72 is present in agiven conductive layer, an open circuit is formed in the conductivelayer at the crack location. As a result, current flow across the cracklocation will be impeded and the resistance of that layer will increase.The increase in resistance of the cracked conductive layer can bedetected by control circuitry 24 and appropriate action taken.

If desired, terminals (busbars) 62 may extend horizontally along the topand bottom edges of window 16 (parallel to dimension X), as shown in theexample of FIG. 8. FIG. 9 shows how terminals 62 may extend verticallyalong the left and right edges of window 16 (as an example). Otherconfigurations may be used, if desired. For example, terminals 62 may beprovided within interior portions of the footprint of window 16, mayhave curved shapes, may have non-elongated shapes, etc.

FIG. 10 shows how segmented terminal configurations may be used inwindow 16. In the example of FIG. 10, segmented terminals 62′ (e.g.,strips of metal or other elongated conductive structures that areshorter than the full-length terminals of FIGS. 8 and 9) may be providedalong one or more of the edges of window 16. Each terminal 62′ maycontact a conductive layer in layer 54 at a different respectivelocation.

By providing multiple segmented terminals along the edges of layer 54,control circuitry 24 may ohmically heat different corresponding regionsof window 16 and/or may make targeted resistance measurements. Crackdetection may be facilitated by making resistance measurements that areperpendicular to the direction of crack propagation. As a result, it maybe desirable to make crack-detection resistance measurements along bothvertical and horizontal directions. A vehicle window may have particularareas that are more prone to icing or condensation than others and/ormay have areas (e.g. a driver-side window area) that are of interest todefrost and deice before others. By segmenting terminals 62′, crackdetection accuracy may be enhanced and ohmic heating operations may beprovided with enhanced flexibility.

As an example, consider a scenario in which it is desired to defrost anarea running along the lower edge of window 16. In this scenario, anohmic heating current can be applied along path 76 between terminals Aand B to ohmically heat the portion of window 16 that lies directlybetween terminals A and B.

As another example, consider a scenario in which window 16 has a cracksuch as crack 72′ that lies parallel to horizontal dimension X. Thistype of horizontal crack may be detected effectively by measuring theresistance between terminals C and D along vertical path 78 parallel toorthogonal dimension Y (as an example).

In general, window 16 may have terminals of any suitable layout(elongated terminals that extend across most or all of the width and/orheight of window 16, segmented terminals along the vertical and/orhorizontal edges of window 16, and/or combinations of these layouts).Each terminal may be coupled to the same conductive layer in layer 54 orone or more of the terminals may be coupled to different conductivelayers in layer 54. For example, one conductive layer may have terminalssuch as segmented terminals 62′ of FIG. 10 and another conductive layermay have terminals 62 of FIG. 8 that each extend across the entire widthof window 16 and that therefore each extend past multiple segmentedterminals 62′. Configurations in which each of two conductive layerseach has a respective set of segmented terminals or in which each of twoconductive layers each have terminals 62 of FIG. 8 and/or FIG. 9 mayalso be used. Terminals 62 off FIG. 8 may be coupled to one conductivelayer and terminals 62 of FIG. 9 may be coupled to the same conductivelayer or another conductive layer. In general, any suitable combinationof horizontal and/or vertical elongated terminals 62 and/or segmentedterminals 62′ may be used.

With multiple terminals, control circuitry 24 has flexibility in makingresistance measurements. For example, control circuitry 24 can cyclethrough different horizontal pairs and/or vertical pairs of segmentedterminals 62′ during resistance measurement operations to help detectand localize cracks 72′. Resistance measurements may also be madethrough one conductive layer using a first set of terminals at the sametime that ohmic heating current is being independently applied through aseparate conductive layer using a second set of terminals. If desired,resistance may be measured by monitoring the voltage rise thataccompanies applied ohmic heating current (e.g., so that both resistancemeasurement operations and ohmic heating operations can be performedsimultaneously using the same set of terminals). Resistance measurementsmay be made periodically (e.g., once per minute) using low power signalsto provide vehicle 10 with continuous crack detection capabilities.Resistance measurements may also be made just before each ohmic heatingoperation is commenced to ensure that the ohmic heating conductive layerhas not been compromised. Ohmic heating operations may be performedautomatically (e.g., when condensation is detected using a moisturesensor, camera, or other detection equipment, based on exterior and/orinterior temperature information, based on weather forecasts that havebeen wirelessly received by control circuitry 24, etc.) and/or may beperformed manually (e.g., in response to a button press or other inputfrom a user of vehicle 10).

FIG. 11 is a flow chart of illustrative operations involved in usingwindows 16 in vehicle 10. Vehicle 10 may have a window 16 with one ormore conductive layers and these layers may be used, for example, informing infrared-light-blocking filters. Control circuitry 24 may becoupled to the conductive layers using one or more pairs of terminals64. The terminals may be segmented as described in connection with FIG.10 and/or may extend across the entire width and/or height of window 16as described in connection with FIGS. 8 and 9.

To ensure that cracks in window 16 are detected, control circuitry 24may measure the resistance of one or more conductive layers in window 16during the operations of step 80. If desired, other electricalproperties of window 16 may be measured (e.g., capacitance measurementsmay be made, inductance measurements may be made, etc.). The resistancemeasurements (or other electrical measurements) may be compared tothreshold values (e.g., to determine whether measured resistance exceedsa predetermined threshold resistance), may be compared to movingaverages and/or other historical resistance information, and/or may beprocessed using other techniques to determine whether or not theresistance of the conductive layer(s) is normal or is abnormal (i.e.,abnormally high). If the electrical characteristics of the measuredconductive layer are normal (e.g., the resistance for window 16 isnormal), control circuitry 24 can conclude that there are no crackspresent in window 16.

If the resistance of window 16 is normal and if a user or automaticprocess running on control circuitry 24 desires to ohmically heat someor all of window 16, control circuitry 24 can apply ohmic heatingcurrent to one or more selected portions of one or more conductivelayers in layer(s) 54 of window 16 at step 82. If desired, ohmic heatingcan be localized by applying ohmic heating current using segmentedterminals. Ohmic heating current may be applied through the sameconductive layer that was monitored during the resistance measurementsof step 80 or may be applied through one or more other conductive layersin window 16. If no heating of window 16 is needed, the operations ofstep 82 may be skipped. As indicated by line 84, processing maycontinually loop back through step 80, so that window 16 can bemonitored for cracks. During crack detection operations, the applicationof ohmic heating current (if any) can be momentarily suspended or bothcrack-detection resistance measurements and ohmic current heatingoperations may be performed simultaneously.

As shown in FIG. 11, control circuitry 24 can take suitable action atstep 86 in response to detection of an abnormal condition in window 16(e.g., in response to detection of a crack by measuring an abnormallyhigh resistance for a window conductive layer during the operations ofstep 80). As an example, ohmic heating operations can be suspended upondetecting a crack. A user may also be alerted to the presence of a crackby displaying a visual message on a display or presenting an audiblealert or other alert to the user with one or more other input-outputdevices 22. If desired, alerts may be wirelessly transmitted to aportable electronic device or other electronic equipment associated withthe user. For example, control circuitry 24 may send an email message orother message to a user that informs the user of the detected crack andadvises the user to schedule a service appointment for vehicle 10.Vehicle 10 may also schedule the service appointment automaticallywithout intervention by the user or following a brief confirmation fromthe user. Vehicle 10 may have autonomous driving capabilities. In thisscenario, vehicle 10 may autonomously drive to a service facility forservicing (e.g., at night or other time when the user is not usingvehicle 10). In some situations, the detected crack may be extensive,which indicates that window 16 is very damaged. Vehicle 10 may use aninternal camera or other systems to confirm the extent of damage and/ormay deactivate vehicle controls to prevent use of vehicle 10 untilwindow 16 has been repaired. In the event that an unauthorized personbreaks into vehicle 10, the automatic deactivation of vehicle 10 mayprevent vehicle 10 from being stolen or used without authorization andthis feature may therefore serve as a theft deterrent. Control circuitry24 may also alert emergency services, send information to an insurancecompany, send information to a traffic management system, or sendwireless messages to other parties in response to detection of a crackin window 16. Following satisfactory resolution of the operations ofstep 86, processing may loop back to step 80 so that additionalresistance measurements may be made.

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. A vehicle, comprising: a body; a vehicle windowin the body having a blanket thin-film conductive layer and multipleterminals coupled to different respective locations of the blanketthin-film conductive layer; and control circuitry configured to: applysignals to the blanket thin-film conductive layer through the multipleterminals; and make electrical measurements on the blanket thin-filmconductive layer.
 2. The vehicle defined in claim 1 wherein the multipleterminals are distributed along first and second opposing sides of theblanket thin-film conductive layer.
 3. The vehicle defined in claim 1wherein the multiple terminals are distributed along first, second,third, and fourth sides of the blanket thin-film conductive layer. 4.The vehicle defined in claim 1 wherein the blanket thin-film conductivelayer comprises an infrared-light-blocking layer.
 5. The vehicle definedin claim 1 wherein the electrical measurements comprise resistancemeasurements.
 6. The vehicle defined in claim 5 wherein the controlcircuitry is configured to detect a crack in the vehicle window based onthe resistance measurements.
 7. The vehicle defined in claim 6 whereinthe control circuitry is configured to output an alert in response todetecting the crack in the vehicle window.
 8. The vehicle defined inclaim 6 wherein the control circuitry is configured to deactivatevehicle controls in response to detecting the crack in the vehiclewindow.
 9. The vehicle defined in claim 1 wherein the control circuitryis configured to apply the signals to the blanket thin-film conductivelayer to ohmically heat different regions of the blanket thin-filmconductive layer by different amounts.
 10. A vehicle, comprising: abody; a vehicle window in the body having a thin-film conductive layerand segmented terminals coupled to the thin-film conductive layer; andcontrol circuitry configured to: apply a current to a first portion ofthe thin-film conductive layer though the segmented terminals; and makeelectrical measurements on a second portion of the thin-film conductivelayer.
 11. The vehicle defined in claim 10 wherein the thin-filmconductive layer comprises an infrared-light-blocking layer.
 12. Thevehicle defined in claim 10 wherein the electrical measurements compriseresistance measurements.
 13. The vehicle defined in claim 12 wherein thecontrol circuitry is configured to detect a crack in the vehicle windowbased on the resistance measurements.
 14. The vehicle defined in claim10 wherein the control circuitry is configured to apply the current tothe first portion of the thin-film conductive layer to ohmically heatthe first portion of the thin-film conductive layer.
 15. A vehicle,comprising: a body; a vehicle window in the body having a conductivelayer and terminals; and control circuitry configured to: apply acurrent to the conductive layer through the terminals; and makeelectrical measurements on first and second different portions of theconductive layer.
 16. The vehicle defined in claim 15 wherein thecontrol circuitry is configured to apply the current to the conductivelayer to ohmically heat the conductive layer.
 17. The vehicle defined inclaim 15 wherein the conductive layer forms part of a thin-filminterference filter.
 18. The vehicle defined in claim 15 wherein thecontrol circuitry is configured to detect a window crack based on theelectrical measurements.
 19. The vehicle defined in claim 18 wherein thecontrol circuitry is configured to deactivate vehicle controls inresponse to detecting the window crack.